Which of the following isomerism is exhibited by the complexes, $\left[\mathrm{Co}(\mathrm{gly}{)}_3\right]$?

The complex ${\left[\mathrm{Co}(\mathrm{en}{)}_3\right]}^{3+}$ exhibits optical isomerism. Isomerism which is exhibited by the complexes, $\left[\mathrm{Co}(\mathrm{gly}{)}_3\right]$ are geometrical as well as optical as it is not symmetrical. Thus, the correct option is D.